Audio production for television, video, film, and recorded music sales is a large and growing enterprising, the foundation of much of the entertainment industry. Automation in the form of computerization is becoming more and more important as the basis of technical advances in this industry, to provide ability to mix and process more sophisticated and more voluminous audio input and to provide more flexibility in output. Computerization is also seen as a requirement for cost-effective competition. Manual instruments, systems, and techniques are, by comparison, increasingly more expensive to use.
The basic instrument of audio production is the production mixing console, a workstation presenting an interface to a sound engineer through which he or she may condition multiple channels of audio input, and mix the conditioned results into mono or stereo outputs for direct broadcast or for recording. A production mixing console, hereinafter a mixer, typically presents arrays of input devices, such as switches, knobs, and "faders", for an operator to set to condition and route audio signals. A fader is typically a slide rheostat through which an amplitude may be adjusted as a result of the linear position of the input lever relative to a track.
Mixers typically route audio input signals to individual channels, and each such channel has a repetitive layout of switches, knobs, and faders. For example, a single channel can have more than one input, such as a microphone input and an input from an instrument, a group of instruments, or a tape. Using the controls on a mixer an engineer can select microphone, line, and tape inputs, route the inputs to signal conditioning devices like faders and equalizers, and mix and route the output from the conditioning devices as well. There is typically a selective ability to monitor audio signals, such as by headphones, and often a microphone for talkback by the sound engineer operating the console.
Audio mixing, especially with digital techniques and computer control, is historically a rather recent development. When rock-and-roll music was first introduced there was no such device as a mixer. In the fifties, recording was done by direct input. Modern mixing was initiated about the time of the appearance of the Beatles, and the first units were highly individualistic. Through the sixties and early seventies direct audio mixers continued to be developed, and continued to be relatively small units with a few channels and were very unique in layout. In the mid-seventies standards began to appear, especially relative to layout of switches, rotary potentiometers, and faders. With a standard layout it became possible for a sound engineer to go from one studio to another, and take over the functions comfortably.
In the early development and well into the late seventies, mixers were completely manual. The audio signals were routed to the mixer, and directly through the switches, pots, and faders. In the 1980's automation began to appear in professional recording studios. With the continued development of automated audio mixing and the never-ending addition of new I/O features, the circuitry of consoles has become increasingly more complex. More switches, buttons, and dials mean crowded printed circuit boards. Contributing to the problem, the abundant use of pushbutton switches with light-emitting diodes (LED's) has doubled the density of printed circuit boards since separate circuits for the LED component and the signal component are required for each LED pushbutton installed.
A typical audio mixer console today may well have as many as several hundred LED pushbuttons, each having four leads. A large array of such pushbuttons pushes the density of circuitry to unmanageable proportions.
What is needed is means of separating signal circuitry for pushbuttons from the circuitry for lighting the LEDs in the pushbuttons. An arrangement allowing the circuits to be implemented on separate printed circuit boards would reduce the circuit density for each board and allow for expansion for future requirements. Also, the design and production of dense circuit boards is expensive. It would be more cost-effective to produce two simple boards than one complex one.